Long-range battery electric vehicles: GM's biggest effort in plug-in electric vehicles has been the Volt, with a battery pack providing 38 miles of range and then a range-extending engine that produces electric power to drive the car for another 300 miles or so.

That system, called Voltec, is the core of GM's plug-in efforts and is expected to spread across a wider range of vehicles, body styles, and segments in future.

Its sole battery-electric vehicle today is the low-volume Chevrolet Spark EV minicar, with a range of 82 miles. It's hardly a competitor to the large Tesla Model S sedan, with ranges of 208 or 265 miles.

Harris suggested in the interview that buying Tesla would save GM the cost of developing its own electric-car technology.

For several years now, GM has a very large battery lab--which it expanded again last year--to evaluate dozens or even hundreds of the newest cells and rigorously test those that look promising.

Moreoever, GM has repeatedly said it expects to introduce an electric car with a range of 200 miles within the next two or three years, at a cost of $30,000.

It remains to be proven if the company can do so. But if it can, it's unclear that Tesla would provide any lasting advantage.

Lower battery cost: Conceivably, Tesla could provide GM with the lowest per-kilowatt-hour costs for large battery packs. We don't know for sure, because no automaker will confirm pack cost, but it's a relatively plausible assumption.

But GM and Tesla use radically different types of lithium-ion cells. GM, like virtually every other large carmaker, uses large-format cells--from dozens to perhaps 200 of them.

Tesla, on the other hand, uses thousands of specially-designed small "commodity" cells in the 18650 format--a tactic no other carmaker has put into production.

Its current cell supplier, Panasonic, also custom-makes cells specifically to Tesla's requirements, whereas the cells used by GM are more "off the shelf."

The cells it buys from LG Chem for its Chevrolet Volt range-extended electric car, for example, are identical or very similar to the ones that LG Chem also sells to Ford for use in its low-volume Focus Electric.

More Cadillac buyers: In the interview, analyst Harris suggested that adding Tesla to GM dealerships would "lull people into a Cadillac," meaning that additional shoppers drawn in by the allure of an electric Tesla might be persuaded to buy a Cadillac.

At least so far, however, we've seen no data that suggests that buyers are cross-shopping the Tesla Model S against any Cadillac model.

We'll see how the $76,000 2014 Cadillac ELR range-extended electric coupe fares in the market this year, though GM has said it expects to sell only 2,000 to 4,000 of them.

Luxury brand: Tesla has definitely succeeded at one of the hardest tasks in the auto industry: building a credible brand from scratch that includes a vehicle with attractive styling, good performance, comfortable ride, and a sales and service experience that owners rave about.

The combination of that ownership experience and Tesla's unique technology image are a hugely valuable asset. Perhaps more than technology, it's why Tesla Motors would be an alluring purchase target for another automaker.

Tesla has ambitions to be a mass-market brand, providing electric cars at a variety of price points, but for the moment it's largely viewed as a luxury brand--since its cars curently start at $69,900.

Harris said buying Tesla would get GM not only the company's electric-car technology, but a genuine luxury brand in the bargain: "It's everything GM needs to build upon."

The challenge for GM is how the Tesla brand would fit into its slimmed-down global brand portfolio of Chevrolet, Buick, and Cadillac (plus GMC in North America).